C. Martin

Closed form approximations of the outage capacity and the mutual information between the in- and outputs of a multi-input, multi-output (MIMO) narrowband system in the presence of correlated fading are considered. First, the limiting distribution of the squared singular values of the channel matrix is derived as the number of antennas at either the transmit or receive site increases. Spatial correlation is allowed according to a realistic stochastic channel model and correlation is allowed between the transmitted signals. The derived limiting distribution has the advantage of being closed form while simulations indicate that it provides a reasonable approximation of the true distribution also for realistic antenna array sizes. Second, the channel outage capacity is derived from the limiting distribution above for the case when the number of transmit antennas is large. The resulting outage capacity has a simple form and allows for spatially correlated channel elements as well as correlation among the transmitted signals. Results from simulations and channel measurements are presented that indicate that the derived expression provides an accurate approximation of the true channel outage capacity for a wide range of realistic system conditions.

Summary form only given. Multiple antennas at both the transmitter and receiver have the potential to significantly increase the capacity of a wireless communications channel. That is, using multiple-input (MIMO) techniques with these antennas, multiple independent channels can be supported in the same bandwidth, but only if the scattering environment is rich enough. Recent research has shown that high theoretical capacity is possible-data rates as high as 40 bits/s/Hz have been demonstrated (in an indoor slow fading environment). However, in cellular mobile radio, the channel differs in several important ways from the indoor channel. Therefore, to determine the potential of MIMO techniques for 3G and 4G wireless systems, we conducted the first field tests to characterize the mobile MIMO radio channel in a typical cellular environment. We present field test results showing the potential increase in capacity using 4 transmit and 4 receive antennas at both the base station and terminal in a mobile environment.

In this paper we present results from the first field test to characterize the mobile multiple-input multiple-output (MIMO) radio channel. We measured the capacity, normalized to a single antenna system for different antenna configurations using 4 transmit and 4 receive antennas at both the base station and terminal in a mobile environment. We compare results for a base station rooftop antenna array consisting of dual-polarized spatially separated antennas, a vertically-polarized multibeam antenna array, and a dual-polarized multibeam antenna array. The field test results show that close to the theoretical 4 times the capacity of a single antenna system can be supported in a 30 kHz channel with dual-polarized, spatially-separated base station and terminal antennas.

Optimal maximum likelihood detection of finite alphabet symbols in general requires time consuming exhaustive search methods. The computational complexity of such techniques is exponential in the size of the problem and for large problems sub-optimal algorithms are required. To find a solution in polynomial time, a semidefinite programming approach is taken to estimate binary symbols in a general linear system. A condition under which the proposed method provides optimal solutions is derived. As an application, the proposed algorithm is used as a decoder for a linear space-time block coding system and the results are illustrated with numerical examples.

We describe the algorithms, implementation, and laboratory performance of a real-time four element adaptive antenna array testbed for the uplink of a 1.9 GHz IS-136 PCS base station. Using our enhanced direct matrix inversion algorithm, experimental results show nearly a 6 dB higher gain at a 10/sup -2/ bit error rate (BER) with four versus the typical two receive antennas and operation at close to a 10/sup -2/ BER even with an interferer of equal strength to the desired signal at 60 mph fading rates, These results demonstrate the feasibility of using adaptive arrays to increase both the range and capacity of TDMA cellular systems.